Tuner for multiresonators



Aprll 8, 1947-. H. D. HAGSTRUM 2,418,469

TUNER FOR MULTI-RESONATOR Filed May 4, 1944 2 Sheets-Sheet 1 F IG?INVENTOR H. D.HAGS7'RUM ATTORNEY April 8, 1947.

H. D. HAGSTRUM TUNER FOR MULTI-RESONATOR Filed May 4, 1944 2Sheets-Sheet 2 in Q:

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lNl/ENTOR P H.D.HAG$TRUM ATTORNiV Patented Apr. 8, 1947 T7. .11

TUNER FOR MULTIRESONATORS Homer D. Hagstrum, New York, N. Y., assignorto Bell Telephone Laboratories, Incorporated, New York, N. Y., acorporation of New York Application May 4, 1944, Serial No. 534,019

Claims. 1 This invention relates to arrangements for tuning anelectromagnetic resonator of the cavity type and especially to devicesadapted for simultaneously and uniformly tuning the several cavities ofa multicavity resonator. The invention is particularly applicable tomicrowave apparatus.

- The needfor tuning a cavity resonator may arise in many situationsinvolving the handling of microwaves, as in the generation andtransmission of such waves. It iscustomary where power outputs ofseveral kilowatts are required, to generate microwaves in a magnetronoscillator which employs a multicavity resonator.

While the oscillating system' of the magnetron may be predesigned tooperate approximately at a desired frequency, itis desirable to be ableto adjust the operating frequency after the oscillator has beenconnected to a transmission system. One reason for this is that theoperating frequency of a system made up of an oscillator and aload,which system may also include an intermediate transmission mediumtherebetween depends not alone upon the dimensions of the oscillator butalso upon the impedance presented to the oscillator by the load and anysuch transmission medium. Oscillators have in certain cases beenproduced in quantity, inspected and tested in a standardizedtransmission circuit and those oscillators operating outside aprescribed frequency band have been rejected as unsatisfactory. Of theoscillators passing such a test, some operate in the test circuit at afrequency close to one edge of the hand. These marginal oscillators,when placed in the system for which they ultimately are intended, whichsystem may differ somewhat from the test circuit in its impedancecharacteristics, may operate at a frequency outside the band limits, andbe unsatisfactory for that reason. An oscillator which is off frequencycan usually be brought to operate within the band by a small change inthe resonating properties of the oscillator. Other reasons for tuningthe oscillator are to permit a selection of the final operatingfrequency and to permit the frequency to be changed from time to time asdesired. A further reason is to enable manufacturing tolerances to berelaxed while insuring a commercial product which readily can be made tooperate within its prescribed frequency band.

In accordance with the invention, means are provided for altering theshape of a single cavity or of one or more of the cavities of amulticavity resonator. For tuning, over. a wide frequency the cavitiesof a, multicavity resonator is dc sirable as the range which may becovered .is many times that which maybe covered by tuning one cavityalone.

It is often important, in operating a multi-' cavity magnetron, tomaintain as nearly as possible a symmetrical pattern of electric andmagnetic fields. In this way, operating conditions in the respectiveindividual cavities may be keptsimilar. For this purpose, means arepro-. vided in accordance with the invention whereby a plurality,preferably all, of the cavities of a multicavity resonator are tuned ina manner. that is uniform for all the cavities affected. Mechanicalarrangements are shown for simultaneously tuning the several cavities.

In the drawings,

Fig. 1 is a fragmentary view of a. multicavity resonator with means fortuning one of the cavities;

Fig. 2 is a sectional view, in perspective, of a multicavity magnetronhaving a tuning element for simultaneously tuning the individualcavities;

Fig. 3 is a plan view, partly broken away, showing a magnetron like thatof Fig. 2 together with means for adjusting the tuning element fromoutside the vacuum chamber of the magnetron;

Fig. 4 is a fragmentary View similar to that shown in Fig. 3 except thatthe tuning element is shown moved with respect to its position in' Fig.3;

Fig. 5 is a cross-sectional view of the magnetron shown in Figs. 2, 3and 4;

Fig. 6 is a plan view of a tuning element of a different shape from thatshown in Figs. 3: and 4; and

Fig. 7 is a fragmentary view, showing a modified form of tuning systemin accordance with the invention.

Referring now to Fig. 1, a fragment of a multicavity resonator It isshown, in section, including two individual resonating cavities l9.Extending radially into one of the cavities I9 is a tuning rod or screw80, which may be adjusted to any desired position. The tuning of thecavity containing the screw is affected by the position of the screwtherein and, due to the presence of coupling between the adjacentcavities IS, the position of the screw 80 is found to affect materiallythe tuning of the multicavity resonator as a whole. The couplingarrangement is more fully described hereinafter incon:

nection with Figs. 2, 3, 4 and 5. Provision may be made in well-knownmanner for retaining vacuum within the cavities of theresonator whilemaking the element 80 adjustable from outside the evacuated space. Anexample is shown employing a. metallic bellows for such a purpose, inFigs. 3, 4 and '7. l

In Figs. 2,3, 4. and 5, the principal working parts of a magnetronoscillator are shown so as to more fully explain how the invention is tobe embodied in an oscillator and to show how a plurality of tuners maybe operated simultaneously. The oscillator has an anode it which may bea perforated metal block fitted snugly within a vacuum-tight container,the latter comprising a side wall portion II, and end plates I2 and I 3.In a central perforation H! in the anode block there may be mounted acathode M which may contain a heating element and be supported by wiresor conductive rods I5 and I5 entering the vacuum. chamber throughsuitable dielectric seals H and It, respectively, p

The-anode l0 comprises a multi'cavity resonator having a plurality ofindividual resonating cavities 19 each connected through a slot 26 withthe central perforation iii, the portions H of the anode blockbetweenadjacent slots 26 forminganode segments in well-known manner. End spaces2| and 22: are: provided. between the ends of the anode. ill: and the.plates 12 and it, respec-' tively. The spaces 2! and 22, together withthe slots 2%? and the anode-cathode space comprising the. perforation1B, serve to provide electromagnetic' coupling betweenth-e individualcavities it. An. initial steady potential: difference between the anode1e and the cathode l4 may he provided in any suitable manner as by meansof a pulsing generator or other source and represented here forsimplicity as a battery 23, the positive terminal of which may beconnectedv to the casing of the magnetron and grounded as at 25. Heatingcurrent may be supplied to the cathode through the conductors It and i6from a suitable source such as a. battery 25, the cathode being heatedeither directly or indirectly, as desired. An initial steadymagnetomoti-ve force in a direction substantially parallel tothe'c'athode may be supplied in any suitable manner.

A set of. connectors or straps 2%) may be used to interconnect the anodesegments according to any desired scheme for the purpose of favoring oneparticular mode of. oscillation among several possible modes ofmu'ltiresonant system, as has become customary in this art. 7

1 The magnetron oscillator shown is of the-general type disclosedin U. S..Patent 2,0633% issued. December 8, 1935, to A. L. Samuel. Variousarrangements areknown in the art for lea-ding oiT electromagnetic wavesgenerated within an oscii-- lat'or oi this type and supplying themto atransmission system or utilization circuit. Any suitable output devicemay be employed with: the oscillator disclosed and will be readilysup-plied by one skilled in this art.

In the arrangement .of Figs. 2, fieand 5, a rotatable' tuning elementtil isprovided which passes through or projects into several, andpreferablya ll',.of the individual cavities 19; The element 353 may hein the form of a ring composed of two parts joined together by screws(i-l and 3-2 as shownin Fig. 3; The ringtil is preferably assem bled. ina peripheral: 01 circurnfererrti'al' groove: 33 which may be: cut"intothe anode: hl'o'ck i9 as: by turning; in: a lathe. Bearing surfacesmay be provided as by means of 1 shoulders at 81 and B2 The position ofthe element St in the groove 33 may be seen in Fig, 2. The grooveintersects the individual tuning cavities, making a plurality of tuningopenings preferably arranged in a circular array about the central axisof the opening 16. A portion or segment of the element 30 projects intothe individual cavity [9. The inner edge or surface of the element 30preferably has a non-circular outline orcontour of a pattern whichrepeats itself the same number of times as their individual cavities l9so thatwhen the element 39 is rotated about the central axis of themagnetron, the amount and disposition of the material projecting intothe cavity I9 is the same for each cavity but varies according to theangular position of the element 39. Figs. Band 4 show a plurality ofcircular scallops arranged in radial symmetry on the inner edge of theelement 35, one extreme angular position being indicated in Fig. 3 inwhich the scallops are centered upon. the individual cavities.- Fig. 4shows the element 38 rotated approximately 22 /2 degrees which is thecorrect displacement in the case ofa resonator with eight symmetricallyspaced cavities as shown, to withdraw the scallopedportion of theelement 36 entirely within the anodeblock Ill. By rotating the element36, any intermediate position between those shown in Figs. Sand-4,respectively, may be obtained, the effect of rotat-- ing. the elementBil being to vary the tuning. properties of all the cavities i9simultaneously and in the same degree.

Any suitable mechanical means may be ,sup-' plied for rotating theelement 30' from outsidethe vacuum chamber. In Figs. 3 and 4 there isshown by way of example, a tangential rod 49 with a bent end engaging anotch 4|- in the outer edge of the element 30. To maintain the vacuum,the rod may be manipulated through any suitable flexible closure such asa bellows d2, preferably of metal and sealed over an opening, d3 bywhich the rod 40 passes through the wall ll. Suitable. means such as athumbscrew 44- coupled to the rod 4%! through a ring 45 rotatablysecured in a groove it may be provided for controlling the motion of therod 40 and the thumbscrew 44- may be supported as by a bracket 4,1,secured to the wall H.

It will be evident that rotation of the thumb;- s'crew' 44' will causeaxial motion of. the rod 40 tangentially with respect to the element 30;which will inturn produce rotation ofthe element '30" and variation ofthe tuning in all thecha-Inbers l5, simultaneously. a

Figs 6 illustrates the useofatuning element 50,- similar to the element39 except that the element has a serrated inner edge. Itwill be evidentthat rotation of the elementEil willeproduce simultaneous; tuning ofall-the chambers!!! exactly-as in the case of the element 30, exceptthatthe variation in. the tuning with respect to; the angular displacementof the rotatable element-will fol-- low a' somewhat different law. inthe-two cases; 7

Fig. 7 shows another modificationo'f the tuning;

- system in which antindiv-idual tuning. rod or plunger Si] is providedprojecting into-each resonating; cavity [9. In this case all-the rodsare operated simultaneously by means of arotatable element 61'containing'a series of inclinedslots 62 each of whichengages andcontrols thgmotion of a pin 63 attached to oneot the; rods 60. It willbe evident that the element 6| mechanically 'intercouples the" rods andt1'1"a=t-'v rotation. of

the element GIIWHIZGHUIS'ET the rodste move-radially with respect to thecavities 1 9, thereby'tuning;

all the cavities simultaneously. In Fig. 7, the extreme inner and outerpositions of the rods are indicated by broken lines.

It will be evident to those skilled in this art that other suitablemeans are known for rotating a part, such as the tuning element herein,from outside a vacuum chamber, for example, a lever arrangementsupported by a flexible diaphragm may be employed. It will also beevident that the rotatable tuning element might be placed at the top orbottom of the anode plate Ill instead of being arranged in a slot 33.The tuning element would then control the size and shape of the openingbetween the individual cavity l9 and the adjacent end space. The elementcould be rotatably supported in the end space in any suitable manner.This latter arrangement would be appropriate in case it was desired tohave the out,- put coupling inserted centrally into one of the cavities[9 in a radial direction, as is commonly done. a

The material of the tuning element 39, 50 or 60 may be conductive suchas solid metal, or it may be any suitable material metalized or coveredwith a conductive coating of suitable depth to confine Within the cavityelectromagnetic waves of the desired operating wavelength. On the otherhand, the tuning element may be partly or wholly composed of adielectric material so as to vary the electric properties of the spacewithin the cavities.

What is claimed is:

l. A resonator comprising a member containing a plurality of individualresonating cavities arranged in radial symmetry about a central axis,and a tuning element rotatable about said axis, said tuning elementhaving a plurality of non-circular portions each extending into one ofsaid resonating cavities by a variable amount depending upon the angularposition of the tuning element.

2. A resonator containing a plurality of resonating cavities each havinga tuning opening, said openings being positioned in a circular arrayabout a central axis, and a tuning element rotatably mounted withrespect to said central axis, said tuning element having a non-circularcontour defining a plurality of segments each extending into one of saidresonating cavities through the respective tuning opening by a variableamount depending upon the angular position of the tuning element.

3. A resonator comprising a member contain ing a plurality of individualresonating cavities arranged to have radial symmetry about a centralaxis, and a tuning element rotatable about said axis, said tuningelement having a serrated edge the respective teeth of which projecteach into one of the said individual cavities, whereby the tuning of theresonator depends upon the angular position of the tuning element.

4. A resonator comprising a, perforated block containing a plurality ofindividual resonating cavities arranged in a circular array about acentral axis, and a tuning element rotatable about said axis, saidtuning element having a plurality of segments each extending into one ofsaid resonating cavities by a variable amount depending upon the angularposition of the tuning element.

5. A resonator comprising a perforated cylindrical block containing aplurality of individual resonating cavities arranged in radial symmetryWith their axes parallel to the cylindrical axis of said block, theblock having a circumferential groove in its outer surface, said grooveintersecting each of said individual cavities, and an annular tuningelement rotatably mounted in said groove, said tuning element having anoncircular inner surface the contour of which has a plurality ofprojections as numerous as the individual cavities in the resonator,whereby rotation of said tuning element simultaneously varies the tuningproperties of the several individual cavities.

HOMER D. HAGSTRUM.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,294,942 Varian et a1 Sept. 8,1942 2,356,414 Linder Aug. 22, 1944 2,323,729 Ryan July 6, 1943

